I suppose that's one definition of expertise. I try to learn more and more about more and more.

My point, however, is that a doctor's degree in, say, engineering will focus on some obscure aspect of engineering, such as predicting chemical erosion as a failure mode in airframe components. Nothing in that student's course of study will necessarily test his knowledge about the scientific method, categorical logic, inductive or deductive reasoning, or any of the other aspects of epistemology that characterizes what we would expect from a "doctor of philosophy".

I guess that is the longer version of what you said: someone will know a lot about how airplanes fall apart, but not a whole lot about how to think clearly when confronted with evidence.